reference · Forex & currencies
Lots, Units and Contract Size: Translate Quantity Into Exposure
A lot is a quantity convention defined for an instrument or platform. Units describe the underlying amount, while a contract's specifications determine its size and money response to price. Equal displayed quantities need not mean equal exposure.
Key points
- Use the actual symbol's contract-size definition rather than a global lot assumption.
- Convert to underlying units or money per price unit before comparing instruments.
- Validate minimum, maximum and step rules after the economic quantity is calculated.
Scope and assumptions
- The FX calculation assumes a symbol explicitly defined as 100,000 base-currency units per lot. Futures examples use the cited contract multipliers rather than that FX convention.
Quantity needs an instrument definition
A quantity field is meaningful only with its unit. MetaTrader exposes contract size alongside volume constraints in its symbol specification. Spotware provides separate conversions between lot quantity and volume in units in its Symbol API. These are reasons to read the actual symbol rather than carry one lot definition across all markets.
For an FX instrument whose specification states 100,000 base units per lot, the calculation is base units = lots × units per lot. For other products, the economic meaning of contract size can be ounces, barrels, shares or a currency multiplier per index point.
A decimal lot becomes an exact unit amount
With the explicit 100,000-unit assumption, 0.37 lots represents 37,000 base-currency units. At a hypothetical quote of 1.1000 quote-currency units per base unit, its quoted notional is 37,000 × 1.1000 = 40,700 quote-currency units.
| Input or result | Value |
|---|---|
| Quantity | 0.37 lots |
| Specified lot size | 100,000 base units per lot |
| Underlying amount | 37,000 base units |
| Quote | 1.1000 quote units per base unit |
| Quoted notional | 40,700 quote units |
The 40,700 figure is not the required margin and is not a maximum loss. It is an exposure measure under the specified quote convention. A one-pip change of 0.0001 would produce 3.70 quote-currency units of linear P&L before costs.
Futures use another useful comparison
For E-mini and Micro E-mini S&P 500 futures, CME specifies $50 and $5 per index point respectively. One ES contract and ten MES contracts therefore both change by $50 for a one-point move, before costs. This is an equality of linear price exposure, not an assertion that their order books, commissions or realized fills are identical. The ES and MES guide works through those differences.
When instruments track different underlyings, matching money per point does not create a hedge or an equivalent strategy. Their prices can move differently. Compare economic identity before trying to normalize quantity.
Apply trading constraints after the conversion
An economically desired amount may not be tradable. Read the destination's minimum quantity, maximum quantity and increment, then apply a deliberate rounding policy. A fractional futures result may require a smaller contract or no trade; it cannot automatically become a fractional exchange contract.
Keep the requested source quantity, unit conversion, desired destination amount and accepted amount in a worksheet. The volume-rounding reference shows how even a small step can create a substantial percentage difference. For copied trades, that residual difference should remain visible rather than being described as an exact match.
Recalculate after a symbol change, contract roll or broker specification update. A conversion that was valid for one instrument snapshot is not permanent evidence that a later symbol has the same size.
Keep contract size separate from the minimum order size. The former defines what a lot or contract represents; the latter defines the smallest quantity the account can request.
Questions and answers
Is one lot always 100,000 units?
No. That is a familiar FX convention, but the actual instrument's specification controls. CFDs, exchange products and broker-specific symbols can use different contract sizes.
Does one MES contract equal one ES contract?
No. Their point multipliers differ by ten to one. Ten MES contracts have the same linear dollar-per-point exposure as one ES contract for the same index move, before differences in fills and costs.
Can I copy the same lot number between different brokers?
Only after verifying that the instruments, sizes, price conventions and account rules produce the intended exposure. A matching number or symbol name is not sufficient.
Sources and further checks
Use the current source for your exact instrument, account and platform. Referencing a general specification does not establish support for every TradeCopier workflow.
- MetaQuotes: Symbol Properties · Checked September 19, 2026
- Spotware: Symbol API · Checked September 19, 2026
- CME: Micro E-mini Equity Index Futures Overview · Checked September 19, 2026
- CME: About Contract Notional Value · Checked September 19, 2026
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